I originally used a Lenovo ThinkServer with Linux Mint for this task. I ended up buying this turn key server from Ebay:
https://www.ebay.com/itm/331173548772?hash=item4d1b7b52e4:g:vqoAAOxycD9TRGzm&amdata=enc%3AAQAHAAAA4PQQNO3AvHzyquJ372Ze8YjXx2brIdKil8TIWXsQPB1lKpCvdDxH3wcWha1Xm2FsrgOHmVLbyHRS4VbD711B26o%2B1VDZz2n8zCa1BFg%2FmlPb7IZy41H1hAV1L83QgnHEsZFJOfjZ3EVepS5OXwXvMiXV%2FZVV61Avvidn6ldmvUyqsKu4LKN33K3I7lcloezTvsQrFdjapOm0tnKZn%2FaCTvea%2F%2B1WQ2FJW56r6ShBNuzSt5VU9I6u8y8WmmMnP6OPEA5nYutE%2Fx%2BchYjLfteZSKH%2BJcf8jvI5MEJXqzSWenE7%7Ctkp%3ABFBM3trVs6Vh
" FreePBX Asterisk Open Source M818-41 1U Cube VoIP PBX Expandable 1G 250G Basic FreePBX Asterisk Intel Atom CPU 1U Cube Mount Open Source VoIP PBX SKU: M818.410.1G250G What's Included Memory 1GB Hardisk 250GB Expansion None Software Asterisk Open Source "
This was cheap and painless to get started. Within minutes I had unique extensions ready to call eachother!
After calculating and taking into account the bandwidth I have access to, each box can comfortably allow for 45+ simultaneous calls. It's cheap enough that I can easily obtain new ones as I expand and put them in my machines room.
This is the part of the service that manages, numbers, voice mails, call quality, call routing. This is the backbone.
